Hydraulic remote for a medical fluid injector

ABSTRACT

A hand-held remote for a medical fluid injector includes a syringe and a conduit which may be coupled to a pressure transducer on a control circuit of the injector. Movement of a plunger within a syringe body on the syringe creates a pressure which is sensed by the pressure transducer and the control circuit responds to the sensed pressure by causing fluid to be ejected from, or drawn into, a syringe mounted to the injector. The pressure developed by the remote provides tactile feedback to an operator for improved control over injections.

FIELD OF THE INVENTION

This invention relates to injectors for injecting fluid into livingorganisms.

BACKGROUND OF THE INVENTION

In many medical environments, a medical fluid is injected into a patientduring diagnosis or treatment. One example is the injection of contrastmedia into a patient to improve CT, Angiographic, Magnetic Resonance orUltrasound imaging, using a powered, automatic injector.

Injectors suitable for these and similar applications typically must usea relatively large volume syringe and be capable of producing relativelylarge flow rates and injection pressures. For this reason, injectors forsuch applications are typically motorized, and include a large, highmass injector motor and drive train. For ease of use, the motor anddrive train are typically housed in an injection head, which issupported by a floor, wall, or ceiling mounted arm.

The injection head is typically mounted on the arm in a pivotal manner,so that the head may be tilted upward (with the syringe tip above theremainder of the syringe) to facilitate filling the syringe with fluid,and downward (with the syringe tip below the remainder of the syringe)for injection. Tilting the head in this manner facilitates removal ofair from the syringe during filling, and reduces the likelihood that airwill be injected into the subject during the injection process.Nevertheless, the potential for accidentally injecting air into apatient remains a serious safety concern.

In addition to the injection head discussed above, many injectorsinclude a separate console for controlling the injector. The consoletypically includes programmable circuitry which can be used forautomatic, programmed control of the injector, so that the operation ofthe injector can be made predictable and potentially synchronized withoperations of other equipment such as scanners or imaging equipment.

Thus, at least part of the injection process is typically automaticallycontrolled; however, the filling procedure, and typically some part ofthe injection procedure, are normally performed by an operator, usinghand-operated movement controls on the injector head. Typically, thehand-operated movement controls include buttons for reverse and forwardmovement of the injector drive ram, to respectively fill and empty thesyringe. In some cases, a combination of buttons is used to initiatemovement of the ram or to control ram movement speed. The injector headalso typically includes a gauge or display for indicating injectionparameters to the operator, such as the syringe volume remaining, forthe operator's use when controlling the injector head.

In many cardiology procedures, cardiologists often prefer to usehand-held syringes to administer contrast media to a patent whereby thecardiologist can “feel” the injection and carefully control the rate ofinjection as needed. Because a high pressure is required to pushcontrast media through a catheter, small hand syringes must be used ifan operator desires to manually administer the contrast media. However,these small syringes must be refilled several times during the contrastinjection procedure, thereby increasing the risk of introducing air intothe syringe or catheter.

U.S. Pat. No. 6,221,045 to Duchon et al. discloses a hand-held remotewhich may be used to control the injection of contrast media with apowered injector. If an operator chooses to use a powered injectorhaving conventional controls, the operator must rely on visualindicators from the injector to determine how to manipulate the controlfor optimum injection. The visual indicators typical of current injectorsystems do not provide operators with the physical sensing of theinjection that they prefer. Thus, one drawback of current injectorsystems, including the hand-held control system of Duchon et al., isthat they do not permit operators to physically sense the injections andthereby control the rate and volume of the injection.

Due to sterility requirements in medical environments, hand-heldcontrols are typically provided as disposable items. Thus, anotherdrawback of conventional hand-held controls which utilize electronic ordigital signals to control the injections is that they are notdisposable without prohibitive expense.

A need exists for a hand-held remote which may be used with a poweredmedical injector to control the injection of contrast media whileproviding tactile feedback to the operator and which solves variousproblems in the art, such as those mentioned above.

SUMMARY OF THE INVENTION

The present invention provides a simple and convenient means forremotely controlling the injection or aspiration of fluids into or outof a patient using a medical fluid injector while providing tactilefeedback to the user of the medical fluid injector. In an exemplaryembodiment, a hydraulic remote for use with a medical fluid injectorincludes a syringe with a plunger slidably disposed within the syringebody, a pressure transducer which may be coupled to the control circuitof a medical fluid injector, and a conduit which connects the syringe tothe pressure transducer. As used herein to describe the remote, the term“hydraulic” refers to the use of a fluid, which may be a liquid or agas. Accordingly, the hydraulic remote could also be described as apneumatic remote. Movement of the plunger into and out of the syringebody causes a change in pressure within the syringe body. The pressuretransducer senses this change in pressure through the conduit and thecontrol circuit of the medical fluid injector responds to the change inpressure by injecting or withdrawing fluid from the patient. Thepressure in the syringe may also be sensed by the user of the hand-heldremote such that the remote provides a tactile feedback to the user thatis indicative of the rate and volume of injection or aspiration. Thesyringe and conduit may be inexpensive, off-the-shelf items, therebyminimizing disposal and replacement costs.

In another exemplary embodiment, a medical fluid injector includes ahydraulic remote, as described above, and further includes a plungerdrive ram, a motor for moving the drive ram, a second syringe attachedto the injector. The plunger drive ram moves a plunger into and out ofthe second syringe to inject or aspirate fluid from a patient. Themedical injector further includes a control circuit which controls themovement of the plunger in the second syringe and responds to pressuresensed by the pressure transducer to move the plunger drive ram into orout of the second syringe. The medical injector responds to an increasedpressure sensed by the pressure transducer by moving the plunger driveram at a rate related to the change in sensed pressure from thehydraulic remote.

In another exemplary embodiment, a medical fluid injector includes ahand-operated control mounted to the injector. A control circuit of theinjector responds to movement of the hand-operated control to move aplunger drive ram into or out of a second syringe attached to themedical injector at a rate corresponding to movement of thehand-operated control. The medical injector further includes a hydraulicremote and the control circuit is configured to respond to actuation ofthe hydraulic remote or the hand-operated control by moving the plungerdrive ram into or out of the second syringe.

In yet another exemplary embodiment, the medical injector furtherincludes a second pressure transducer coupled to the control circuit andto the hydraulic remote. The control circuit responds to pressure sensedby the first pressure transducer to control the motion of the plungerdrive ram into or out of the second syringe. The control circuitresponds to the pressure sensed by the second pressure transducer toenable operation of the medical fluid injector when the pressuretransducer senses a pressure above a preset threshold. Advantageously,the threshold pressure is set at a level such that injection oraspiration of fluid will cease when a user releases the plunger on thehydraulic remote.

In another exemplary embodiment of the present invention, a circuitboard is couplable to an existing medical fluid injector to modify theinjector so that it can be used with the hydraulic remote as describedabove.

In yet another exemplary embodiment, a method of controlling theinjection or aspiration of fluid using a medical fluid injector having ahydraulic remote coupled to the injector includes the steps of moving aplunger of the hydraulic remote to generate a pressure, sensing thepressure generated by the hydraulic remote, and moving a plunger driveram on the injector in response to the sensed pressure.

The features and objectives of the present invention will become morereadily apparent from the following Detailed Description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIG. 1 is a perspective view of an exemplary medical fluid injector withan exemplary hydraulic remote of the present invention;

FIG. 2 is an exploded perspective view of the injector of FIG. 1;

FIG. 3 is an electrical block diagram illustrating the circuitry of thehydraulic remote and hand control of the injector of FIG. 1;

FIG. 4A is an electrical block diagram of interface circuitry connectedto the circuitry of FIG. 3 and other external sensors of the injector ofFIG. 1;

FIG. 4B is an electrical block diagram of the processor and peripheralcircuitry of the injector of FIG. 1; and

FIG. 4C is an electrical block diagram of the watchdog system of theinjector of FIG. 1.

DETAILED DESCRIPTION

The present invention provides a hand-held remote control which may beused with a medical injector to control the injection of fluids into apatient while providing tactile feedback to an operator of the injector.Furthermore, because the disposable components of the remote control areoften available as off-the-shelf items, the cost of the disposable itemsare significantly reduced compared to currently available systems.

Referring to FIG. 1, there is shown an exemplary medical injector 10including an exemplary hand-held remote 12 of the present invention. Onesuch medical fluid injector is the Illumena model injector, availablefrom Liebel-Flarsheim Company, Cincinnati, Ohio. The injector 10includes a power head 14 housing an internal drive motor, ahand-operated movement control lever 16, and a display 18 for indicatingto an operator the current status and operating parameters of theinjector 10. The power head 14 may generally be supported on a carriage(not shown) by a mount 20 and an articulated support arm 22, asdescribed more fully in U.S. Pat. No. 5,925,022 to Battiato et al.,which is commonly held by the assignee of the present invention andherein incorporated by reference in its entirety. A syringe 24 includinga syringe barrel 26 and a plunger 28 may be mounted on the power head 14to interface with the internal drive motor (not shown) of the injector10. The plunger 28 is coupled to a plunger drive ram (not shown) of themotor whereby the motor may cause the syringe plunger 28 to move alongthe syringe barrel 26 to inject contents of the syringe 24 or to drawfluids into the barrel 26 via discharge tip 30. The syringe 24 may besurrounded by a pressure jacket 32 which supports the outer walls of thesyringe barrel 26. A heater blanket 34 may be mounted on a post 36 whichextends from the power head 14, and abuts the exterior wall of pressurejacket 32 to heat the contents of the syringe 24 and maintain thetemperature at approximately body temperature.

Referring further to FIG. 2, the power head 14 further comprises ahousing made up of a first housing portion 40 a and a second housingportion 40 b which enclose the internal drive motor and a controlcircuit 42 for controlling the motor. Manipulation of the hand-operatedmovement control lever 16 is sensed by the control circuit 42 to causethe plunger drive ram to inject or aspirate fluids from the syringe 24,as more completely described in U.S. Pat. No. 5,925,022 to Battiato etal. Alternatively, the injector 10 may be operated using the hydraulicremote 12.

Referring now to FIGS. 1 and 2, remote 12 includes a second syringe 50,conveniently sized to be hand-held, and a conduit 52 connecting anoutlet of the syringe 50 to the injector 10. In an exemplary embodiment,the conduit 52 is a flexible tubing. Conduit 52 is coupled to at leastone pressure transducer 54 which, in turn, is coupled to the controlcircuit 42 of the injector 10. In an exemplary embodiment, the conduit52 is coupled to the pressure transducer 54 by a connector 55 whichextends through an aperture 57 in the housing 40. A second conduit 59extends from the connector to one or more pressure transducers 54. Thepressure transducer 54 may either be provided directly on the controlcircuit 42, or alternatively, may be provided on a circuit board 56 thatmay be connected to the control circuit 42 of the injector 10. Forexample, the circuit board 56 containing the pressure transducer 54 maybe configured to be connected to the control circuit 42 of the injector10 at an interface 58 for receiving input from the control lever 16. Thecircuit board 56 may further include a connector 60 for receiving theinput from the control lever 16 and adapted to be coupled to controllever 16, such as by electrical leads 61. Such a configurationadvantageously permits the medical injector 10 to be operated by eitherthe control lever 16 or the hydraulic remote 12.

Referring now to FIG. 3, circuit details of a power injector inaccordance with the invention can be described. Pressure sensors 54 aand 54 b are active electromechanical transducers, which electricallyform a balanced bridge. The potential across the bridge is reflective ofthe pressure being detected by the sensor 54 a and 54 b. Sensors 54 aand 54 b are each connected to differential amplifiers to apply gain tothe differential voltage produced by the sensor. Differential amplifier78 a is connected to sensor 54 a and produces a voltage, referenced toground, in proportion to the magnitude of the pressure detected bysensor 54 a. (The output of amplifier 78 a is referenced to ground by agrounded connection at the REF input of amplifier 78 a.) Differentialamplifier 78 b is connected to sensor 54 b, and also produces a voltagein proportion to the magnitude of the pressure detected by sensor 54 b.However, the voltage produced by amplifier 78 b is referenced to theanalog voltage obtained from potentiometer 98, for reasons to beexplained below.

The output of differential amplifier 78 a is coupled through aresistance R to the inverting input of a comparator 80. The output ofcomparator 80 is fed back to the noninverting input through a resistance10R, thus introducing a hysteresis in the response of comparator 80. Thenoninverting input of comparator 80 has a voltage of approximately 2.5volts when the output of NAND gate 82 is a logic “low”, thus, in thiscondition, comparator 80 will produce a logic “high” signal whenever theinput from differential amplifier 78 a slews above approximately 2.5volts. The gain of differential amplifier 78 a is set so that an outputof 2.5 volts is achieved whenever the pressure detected by pressuresensor 54 a is above a minimum threshold, indicative of the use of thehand syringe 50 to manually control an injection. This thresholdprevents unintended manual operation of the injector from the limitedhydraulic pressure present in the hand syringe 50 as initially installedon the injector.

When the pressure sensed by sensor 54 a exceeds the desired minimumthreshold, and the output of NAND gate 82 is logic “low”, thencomparator 80 will produce a logic “high” output, which enablesoperation of the hand syringe 50 for manual injection control. Theoutput of comparator 80 is coupled to a NAND gate wired as an inverter86, and the output of comparator 80 and NAND inverter 86 are connectedto the control inputs of an analog multiplexer 88. As a consequence ofthese connections, when comparator 80 produces a logic “high” output,multiplexer 88 delivers an analog signal from the output of differentialamplifier 78 b to line 154. When comparator 80 produces a logic “low”output, multiplexer 88 delivers an analog signal from the wiper ofpotentiometer 99 to line 154.

As elaborated in substantially greater detail in the above referencedU.S. patent of Battiato et al., rotation of the manual hand control 16on the powerhead 14 also controls forward and reverse movement of theplunger. Rotation of the manual hand control is detected by a rotarypotentiometer 98. The manual hand control is returned to a neutralposition by return springs 102 a and 102 b. FIG. 3 illustratespotentiometer 98, which is connected between a reference voltage andground to provide a voltage on line 99 indicative of the rotation ofmanual hand control 16. Return springs 102 a and 102 b of the manualhand control, and a flag/contact connected to and rotating with the handcontrol, also form circuit elements in FIG. 3. Return springs 102 a and102 b are connected with a resistor 110 in a series connection between adigital +5 volt power supply and ground. A signal line 115 extendingfrom between resistor 110 and spring 102 a carries a logic voltagesignal indicating whether a current-carrying electrical contact iscompleted between springs 102 a and 102 b and flag/contact 104. Undernormal conditions, there should be an electrical path through this pathto ground, holding the voltage on line 115 at a low level, indicatingproper operation. However, if one of springs 102 a or 102 b fails, andno longer engages flag/contact 104, this electrical contact will bebroken, and the voltage on line 115 will be elevated to a high level,indicating failure of a return spring. Although both return springs mustfail before lever 16 may unintentionally deflect away from the homeposition, failure of just one spring can be detected by monitoring thevoltage on line 115. Upon initial detection of such a failure, a warningmay be given to the operator, or alternatively, the hand-operatedmovement control may disabled.

The hand control 16 further includes a detent spring 106, whichsimilarly forms an electrical contact in a series connection with aresistor 111; a detent signal line 116 extends from between resistor 111and the detent spring. If control lever 16 is not rotated into thedetent spring, line 116 will be pulled to a high level, indicating thatthe control lever 16 is not at the detent. However, if control lever 16is rotated such that flag 105 contacts detent spring 106, line 116 willbe pulled to a low level, indicating that control lever 16 has beenrotated to the detent. The signal on line 116 may be used in severalways. For example, the signal may be used to calibrate the hand-operatedcontrol so that the angle of lever rotation corresponding to the detentis equal to the ideal fill speed. Alternatively, the signal may be usedto prevent reverse movement of the ram at a speed faster than the idealfill speed. Finally, the signal may be used to establish a “dead zone”of motion, in which the ram will move at the ideal fill speed, whilepermitting the lever to be rotated beyond the “dead zone” to producefaster reverse speeds.

FIG. 3 also illustrates the circuit details of a flag detector 108; alight emitting diode is energized with a bias current via resistor 113;when light passes through the gap in detector 108 and strikes the baseof a phototransistor in detector 108, the phototransistor draws currentthrough resistor 112 to drive a home signal on line 117 to a low value,indicating that control lever 16 is not in its home position. Otherwise,if light is unable to pass to the base of the phototransistor indetector 108, current is not drawn through resistor 112 and the homesignal on line 117 is pulled to a high value, indicating that controllever 16 is in its home position. The circuitry on FIG. 3 can thus usethe home signal on line 117 to determine whether the hand control is inits home position.

Specifically, it can be seen that the home signal is connected through aNAND gate connected as an inverter 82, to a voltage divider comprised ofequal valued resistors 84. The midpoint of resistors 84 is connected tothe inverting input of comparator 80. The noninverting input ofcomparator 80 is connected to the output of differential amplifier 78 a,as discussed above. As a consequence of these connections, when the homesignal on line 117 is low (indicating that the hand control 16 is inuse), the output of NAND gate 82 and the midpoint of resistors 84 willhave a logic “high” value. As a result, the output of comparator 80 willhave a logic “low” value regardless of the signal present at the outputof differential amplifier 78 a. As noted, under these conditions, theanalog voltage on line 99 from the wiper of potentiometer 98 isdelivered through analog multiplexer 88 to line 154. Alternatively, whenthe hand control is in its home position, if the pressure in handsyringe 50 is above the established minimum threshold, then the outputof comparator 80 will have a logic “high” value and the analog voltagefrom differential amplifier 78 b is delivered through analog multiplexer88 to line 154.

As can be seen with the above background, the analog voltage on line 154reflects the desired manual movement, whether indicated by rotation ofthe hand control 16 or by pressure on the hand syringe 50. As notedabove, the voltage produced by differential amplifier 78 b is referencedto the analog voltage on line 99 from the wiper of potentiometer 98.Since the hand syringe 50 is only enabled and may only be used while thehand control 16 is in its home position, this connection causes thevoltage output by differential amplifier 78 b to be referenced to thesame voltage produced by the potentiometer 98 on its wiper terminal 99when in the home position. Thus, the analog voltage produced bydifferential amplifier 78 b deviates from the same baseline voltage asthe analog voltage produced by hand control 16 potentiometer 98.

It will be noted that the detent and safe signals on lines 115 and 116are delivered to the microprocessor shown in FIG. 4B, discussed furtherbelow. A third “home” signal is also delivered to the microprocessor.This signal is produced by a first NAND gate 90, via a second NAND gate92 connected as an inverter, so that the “home” signal delivered to themicroprocessor will have a “high” value whenever the hand control 16 isin its “home” position and the pressure sensed by sensor 54 a is belowthe established threshold (causing comparator 80 to produce a “low”output signal). Thus, the “home” signal output by NAND gate 92identifies those conditions where no manual movement is being requestedeither through hand control 16 or hand syringe 50.

Now turning to FIG. 4A, the electrical circuit details of the airdetection module, and other analog electrical systems, can beelaborated. Specifically, the air detection module incorporates therein,a commercially available synchronous detection circuit 140, whichincludes an internal oscillator generating trigger pulses on line 141,and, contemporaneously with each trigger pulse, detects electricalsignals on line 142 indicating that light has been received at lightsensor 127. So long as light is detected contemporaneously with eachtrigger pulse, a high level signal is produced on line 143. Due to theapplication to which circuit 140 is applied in accordance with theinvention, the signal on line 143 indicates whether air has beendetected in the neck of the syringe 24.

The control circuit of power head 14 may control the light intensityapplied to the air bubble detector, to control the sensitivity of thedetector. To do so, the control circuit produces a pulse width modulated(PWM) digital signal on line 145. This PWM signal is filtered by alow-pass filter circuit 146 to produce an analog control voltage, whichcontrols an adjustable regulator 147 to produce the power signal on line148 for circuit 140.

In response to the trigger signal on line 141, a PNP opto-transistor 149is turned “on”, causing the power signal on line 148 to energize lightsource 126. Thus, the voltage of the power signal on line 148 directlyaffects the intensity of light generated by light source 126.

So that the control circuit may monitor the air detector circuit 140 forpossible failures, the trigger signal on line 141 is connected to thebase of PNP opto-transistor 149 via a light emitting diode in anopto-isolator 150. Accordingly, the opto-transistor in opto-isolator 150will turn “on” whenever the trigger signal is activated, causing a “low”level to appear on line 151. Thus, if the synchronous air detectorcircuit 140 is operating properly and producing periodic triggersignals, pulses will appear on line 151, which can be detected by thecontrol circuit to verify that the oscillator in circuit 140 isoperating properly.

FIG. 4A also illustrates the analog-to-digital (A/D) converter 152incorporated into the power head control circuit for quantizing analogsignals produced by various electrical elements. One such signal is thevoltage produced by the circuitry of FIG. 3 on line 154, which isrepresentative of the rotational position of the fill/expel hand control16, or the pressure in the hand syringe 50. A/D converter 152 convertsthe analog voltage on line 154 to a digital signal on a “SPI” serialinterface bus 156, upon request from the CPU (see FIG. 4B), so that theCPU can determine the position of hand control 16 or pressure in thehand syringe 50 and react accordingly.

Other analog voltages are also input to A/D converter 152. Specifically,a single-chip accelerometer is configured as a tilt sensor 158, toproduce an analog voltage on line 159 indicative of the angle of tilt ofsensor 158. (A suitable single chip accelerometer for this purpose isavailable from Analog Devices of Norwood, Mass. as part no. ADXL05AH.)Sensor 158 is mounted to circuit board 55, and therefore produces anoutput voltage indicative of the tilt of power head 14 relative to thedirection of Earth gravity. This analog tilt signal is converted andinput to the CPU for use, as noted below, in controlling the display andother operational features of power head 14.

A third analog signal is produced by a linear potentiometer 160, thewiper of which is mechanically connected to the plunger drive ram, andmoved in response to movement of the plunger drive ram. Thus, thevoltage of the wiper on line 161 is an analog signal representative ofthe position of the ram between its rearward most and forward mostpositions. This signal is converted and used by the CPU to determine theposition of the ram and, among other things, the syringe volumeremaining.

Two additional analog signals are produced by thermistors 163A and 163b, which are series connected with bias resistors to produce voltages onlines 164 a and 164 b which reflect the temperature of the thermistors.The temperature measurement obtained from these thermistors is then usedto control the power applied through the heater blanket 34 to warm thefluid in the syringe 24. Specifically, the heat power applied to thesyringe is varied proportion to the ambient temperature, as measured bythermistors 163 a and 164 a, to maintain the fluid at the targettemperature, e.g., 30 degrees Celsius.

Thermistors 163 a and 163 b are duplicative, that is, both measure thesame temperature and their measurements are compared to ensure nearagreement. As a result, failure of a thermistor can be detected fromdisagreement between the temperature readings obtained from thethermistors, preventing loss of temperature control.

Thermistors 163 a and 163 b may be mounted internally to power head 14,on circuit board 42. Alternatively, thermistors 163 a and 163 b may beexternal to the housing, to ensure more accurate temperature readings,or both options may be allowed by providing internally-mountedthermistors which can be disabled if substitute externally-mountedthermistors are connected to the power head 14.

As noted above, using thermistors 163 a and 163 b, power head 14controls the heat power applied to the syringe 24 through heater blanket34. To perform this function, the CPU (see FIG. 4B) produces a pulsewidth modulated (PWM) control signal on line 166 which is used tocontrol the heat power applied to the heater blanket filament 120.Specifically, the PWM signal on line 166 is low pass filtered by filter167, producing an analog control signal which controls an adjustableregulator 168. The output of regulator 168 on line 169 is a variablevoltage which is applied across heater blanket filament 120, causingheater filament 120 to produce heat.

An instrumentation amplifier 170 filters and conditions the voltageacross filament 120 to produce an analog output signal on line 171 whichis proportional to the voltage applied to the heater blanket filament120.

A sense resistor 173 is series connected with heater filament 120, sothat the current in heater filament 120 passes through sense resistor173, producing a voltage on sense resistor proportional to the currentflowing through heater filament 120. Sense resistor has a resistancesubstantially smaller than that of heater filament 120, so that thesmall voltage drop across sense resistor 173 is not a substantialpercentage of the voltage drop across heater filament 120.

The voltage drop across sense resistor 173 is amplified and filtered bya gain/filter circuit 172, producing an analog voltage on line 174 whichis proportional to the current flowing through heater filament 120.

Lines 171 and 174 are connected to A/D converter 152, and the voltageson lines 171 and 174 are converted thereby to digital signals which canbe read by the CPU. Accordingly, the CPU can determine the current andvoltage drop across heater filament 120, and use these values todetermine the heat output of heater filament 120. This permits the CPUto perform closed-loop control of the heater blanket heat output, asdiscussed more thoroughly in U.S. Pat. No. 5,925,022.

Referring now to FIG. 4B, the connections to the CPU of the power head14 can be understood. The CPU 175, which may be a 68332 microprocessor,available from Motorola, controls data and address busses 176 connectingCPU 175 to random access memory (RAM) 178 and a flash memory 177. CPU175 also controls an SPI serial interface bus 156 for communicating withA/D converter 152, display 30 and a monitor microcontroller 192. CPU 175further includes an RS-422 serial interface 179 connecting CPU 175 to aCPU in the power pack (see FIG. 4C).

CPU 175 includes a number of digital data input lines for monitoringoperation of power head 14. Specifically, CPU 175 receives the detentsignal on line 116, safe signal on line 115 and home signal on line 117,enabling CPU to receive input on the state of operation of thehand-operated controls (lever and syringe) as discussed above. CPU 175also receives the bubble signal on line 143 from which CPU 175 maydetect air in the syringe neck and take appropriate action, and inaddition, CPU 175 receives the bubble detection oscillator signal online 151, which can be used as noted above to confirm proper operationof the oscillator in the air detection module 122. Further, CPU 175receives the output of flag sensor 63, from which CPU 175 may determinewhether the face plate is securely locked to the housing of power head14. Furthermore, CPU 175 receives digital signals from the threemagnetic detectors 57 a, 57 b and 57 c indicative of which of severalpossible face plates are mounted to power head 14, allowing CPU 175 toadjust its operation accordingly.

CPU 175 also receives digital input signals from parallel rotaryencoders 182, which produce pulse signals on lines 183 a and 183 bindicative of rotation of the plunger drive train. These pulses are usedby CPU 175 to confirm movement of the plunger drive ram. Lines 183 a and183 b are also connected to the power pack (see FIG. 4C) so that thepower pack CPU may perform closed loop control of plunger movement bycounting encoder pulses and comparing the rate of receipt of encoderpulses to a desired rate. A closed loop control is disclosed in U.S.Pat. No. 4,812,724, which is incorporated by reference herein in itsentirety.

CPU 175 also produces multiple digital control signals, including thosenoted above, i.e., the air bubble detector power PWM signal on line 145,and the heater blanket power PWM signal on line 166, both beingpulse-width modulated by CPU 175 to produce desired power levels. CPU175 further produces output signals on lines 187 for illuminating lightemitting diodes in lamp 45 (FIG. 2) which indicate the status ofoperation of the injector. Additional output signals on SPI serial buslines 156 control the display 30.

CPU 175 uses the above-noted inputs and outputs to perform primarycontrol of power head 14 under control of software resident in CPU 175or read from RAM 178. As noted above, CPU 175 is also connected, throughSPI serial bus 156, to a microcontroller 192 which serves as a monitor,for monitoring operation of CPU 175 to ensure the absence of software orhardware failures. (Microcontroller may be a single-chip microcontrolleravailable from Microchip Technologies as part no. PIC16C63.) Monitormicrocontroller 192 performs this function by receiving, through bus156, an indication of the current operational state of CPU 175.

Specifically, CPU 175 indicates, through bus 156, the operating state ofCPU 175, i.e., whether CPU 175 is requesting movement of the plunger ornot, and whether the motion is being requested in response tohand-operated or automatic (programmed) control, and potentially otherspecific information such as the rate of movement that is beingrequested. Monitor microcontroller 192 reads this state information fromlines 156, and compares this information to crucial digital inputsignals from the power head 14, to ensure consistency therebetween.

For example, microcontroller 192 receives the safe signal on line 115and home signal on line 117. If these signals indicate that thehand-operated controls are not being used, then CPU 175 should not begenerating movement under hand-operated control. If a spring has failed(as indicated by the signal on line 115), this should be reflected inthe state of the CPU 175. Therefore, under these conditions,microcontroller 192 reads the state information from bus 156 to ensurethat CPU 175 is not acting inconsistently with the signals from thehand-operated controls.

As a second example, microcontroller 192 receives the output signalsfrom rotary encoders 182 on lines 183 a and 183 b. Microcontroller 192checks these signals to determine whether the plunger drive ram ismoving, to ensure the drive ram is moving only when the state of CPU 175indicates that the drive ram should be moving, and not otherwise.Furthermore, in this connection it should be noted that microcontroller192 receives the door flag signal from door flag sensor 63. If thissignal indicates that the door of power head 14 is other than in thelocked position, CPU 175 should not be requesting movement of theplunger drive ram, and microcontroller 192 confirms this by checking forthe absence of pulses from encoders 182.

Referring now to FIG. 4C, the interaction of the power head 14, powerpack 47 and console 25 can be further understood. Specifically, each ofpower head 14, power pack 47 and console 25 contains a CPU 175, 192 and194, respectively. These CPUs interact through external interfaces toperform control of the injector. For example, the plunger drive ram canbe controlled through the lever 16 on power head 14 (as discussedabove), or can be automatically controlled by an operator enteringprograms for injections using touch screen 33 of console 25 (using CPU194), and then enabling the programmed injection. The injectionparameters such as motor speed and injection volumes will then beproduced by console CPU 194, which communicates with power pack CPU 192to cause these programmed actions to take place. Furthermore, anautomatic injection may be enabled using the touch screen 33, or aninjection may be started using a hand switch or OEM remote triggerconnected to power pack 47. In either case, the appropriate one of CPUs192 and 194 generates an enabling signal to initiate the automaticinjection.

As noted above, the power head CPU 175 is associated with a monitormicrocontroller 192 for monitoring the state of CPU 175 to ensure itsactions are consistent with input signals from power head 14. Similarly,CPUs 192 and 194 are also associated with monitor microcontrollers 196and 198, respectively, which monitor the actions of the associated CPUs196 and 198 to ensure consistent, error free behavior.

Monitor microcontrollers 192, 196 and 198 communicate with each other ina manner which parallels the communication of CPUs 175, 192 and 194.Specifically, the three monitor microcontrollers exchange stateinformation received from their associated CPUs to ensure that the threeCPUs are in similar states of operation, e.g., hand-operated movement,automatic movement, no movement, etc. Furthermore, each of themicrocontrollers receives external input signals to ensure that statetransitions which should occur are, in fact, occurring. Thus,microcontroller 196 receives the hand or OEM trigger signals so thatmicrocontroller 196 can determine when an automatic injection has beentriggered. Microcontroller 198 receives input signals from touch screen33 so it, too, can determine when an automatic injection has beentriggered. Other monitoring functions can be performed, as desired toensure correct and consistent operation of CPUs 175, 192 and 194.

As noted above, power head CPU 175 delivers a control signal to powerpack 47, requesting a ram movement. Power pack 47 contains the motorservo control circuitry for producing an appropriate power signal online 200 to the drive motor M, and to perform closed loop control ofmotor movements in response to encoder pulses on lines 183.

In error conditions, the monitor microcontrollers can discontinue powerflow to the motor M through a hardware disable, represented by switch202 in series with power line 200, thereby ceasing any movement of theplunger drive. This hardware disable ensures that the monitormicrocontrollers can prevent erroneous injection of fluid under errorconditions.

Returning now to FIGS. 1-3, operation of the hydraulic remote 12 can bereviewed. The hydraulic remote 12 may be used to control the injectionof fluids by the medical injector 10 when a plunger 62 on the remote 12is moved into a syringe body 64 of the remote 12. The syringe 50 andconduit 52 are filled with air whereby motion of the plunger 62 createsa pressure which is sensed by the pressure transducer 54. When theplunger 62 is moved further into the syringe body 64, the pressuretransducer 54 senses a positive change in pressure from the remote 12.In response to the sensed pressure, the control circuit 42 of theinjector 10 causes the drive motor to move the plunger drive ram intothe syringe 24 on the power head 14 to expel fluid from the syringe 24.In an exemplary embodiment, the control circuit 42 causes the plungerdrive ram to expel fluid from the syringe 24 at a rate that is relatedto the amount of pressure change sensed by the pressure transducer 54.In another exemplary embodiment, the plunger drive ram is moved at arate proportional to the amount of pressure change.

In the illustrated embodiment, two pressure transducers 54 a, 54 b arecoupled to the control circuit 42 of the injector to sense pressure fromthe hydraulic remote 12. The control circuit 42 responds to the pressuresensed by a first of the pressure transducers 54 b to control the motionof the plunger drive ram into the syringe 24, as described above. Thepressure sensed by the second of the transducers 54 a is compared by thecontrol circuit 42 to a threshold pressure above which the injector 10is enabled and below which the injector 10 is inoperable. Thisconfiguration allows the injections to be stopped when an operatorreleases the plunger 62 on the hydraulic remote 12.

The hydraulic remote 12 may include a feature permitting the plunger 62to be retracted from within the syringe body 64 of the remote 12. Forexample, the plunger 62 may include a thumb ring which permits anoperator to pull as well as push on the plunger 62. Because the syringe50 and conduit 52 described herein may be available as off-the-shelfitems and therefore readily available, these components of the remote 12are relatively inexpensive and therefore introduce minimal cost whenused as disposable items.

Medical injectors which are presently in use may be modified to use thehydraulic remote 12 of the present invention by incorporation of acircuit board 56 having at least one pressure transducer 54, asdescribed above. The circuit board 56 may generally be added to anexisting unit's control circuit 42 to permit the injector 10 to operatewith the hydraulic remote 12 and with minimal or no impact to existingsoftware. FIG. 2 shows an exemplary electronic circuit board, includingat least one pressure transducer 54, which may be added to existingcontrol circuits 42 of medical injectors 10 to enable the injector 10 tooperate with the hydraulic remote 12, as described above.

A method of controlling a medical fluid injector 10 using a hydraulicremote 12 as described above, includes the steps of moving a plunger 62of the hydraulic remote 12 to generate a pressure, sensing the pressuregenerated by the hydraulic remote 12 and moving a plunger drive ram onthe injector 10 in response to the sensed pressure, whereby the medicalfluid injector 10 ejects fluid from a syringe 24 coupled to the injector10 unit. In an exemplary embodiment, the control circuit 42 causes theplunger drive ram to eject fluid from the syringe 26 on the injector 10unit at a maximum rate of about 6 ml/sec in response to a pressuresensed by the pressure transducer 54.

While the present invention has been illustrated by the description ofthe various embodiments thereof, and while the embodiments have beendescribed in considerable detail, it is not intended to restrict or inany way limit the scope of the appended claims to such detail. Forexample, while the medial injector 10 has been described herein as beingconfigured to inject fluids into a patient in response to movement ofthe plunger 62 on the hydraulic remote 12 into the syringe body 64, itis also contemplated that the medical injector 10 could also beconfigured to aspirate fluids from a patient in response to movement ofthe plunger 62 out of syringe body 64. The injector 10 could beconfigured to perform either of these functions, solely or selectively,according to the desired operation. For example, it may be desired toaspirate a small amount of blood from a patent upon initialcatheterization to confirm that the intravascular space has beenentered.

Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus andmethods and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thescope or spirit of Applicant's general inventive concept.

What is claimed is:
 1. A medical injector comprising: a plunger driveram; a motor for moving said plunger drive ram; a first syringeincluding a syringe body and a first plunger slidably disposed withinsaid syringe body; a syringe mounting for attachment of a secondsyringe, said syringe mounting positioning said second syringe relativeto said plunger drive ram to permit said plunger drive ram to engage andmove a second plunger into or out of said second syringe; a controlcircuit controlling said motor to move said plunger drive ram and saidsecond plunger to inject fluid from said second syringe; at least onepressure transducer coupled to said control circuit; a condult having afirst end operatively coupled to said first syringe and a second endcoupled to said pressure transducer, whereby movement of said firstplunger in said syringe body creates a pressure which is sensed by saidpressure transducer and causes said control circuit to actuate themedical injector to inject fluid in response thereto; said controlcircuit responding the pressure sensed by said pressure transducer bymoving said plunger drive ram at a rate related to the sensed pressure.2. The injector of claims 1, further comprising two pressure transducerscouplable to said control circuit.
 3. The injector of claim 2, whereinsaid control circuit responds to the pressure sensed by a first of saidpressure transducers to control the motion of said plunger drive raminto said second syringe, and said control circuit responds to thepressure sensed by a second of said pressure transducers to enableoperation of the injector when the pressure is above a thresholdpressure.
 4. The injector of claim 3, wherein said threshold pressure issufficient to disable operation of the injector when said plunger isreleased.
 5. The injector of claim 2, wherein said control circuitresponds to the pressure sensed by a first of said pressure transducersto control the motion of said plunger drive ram out of said secondsyringe, and said control circuit responds to the pressure sensed by asecond of said pressure transducers to enable operation of the injectorwhen the pressure is above a threshold pressure.
 6. The injector ofclaim 5, wherein said threshold pressure is sufficient to disableoperation of the injector when said plunger is released.
 7. The injectorof claim 1, wherein said control circuit responds to the pressure sensedby said pressure transducer to move said plunger drive ram at a rateproportional to the amount of pressure change.
 8. The injector if claim7, wherein said control circuit moves said plunger drive ram up to amaximum rate of about 6 milliliters per second.
 9. The medical injectorof claim 1, wherein said control circuit responds to increased pressuresensed by said pressure transducer by moving said plunger drive ram intosaid second syringe to expel fluid from said second syringe at a raterelated to the positive change in sensed pressure.
 10. The medicalinjector of claim 1, wherein said control circuit responds to decreasedpressure sensed by said pressure transducer by moving said plunger driveram out of said second syringe to draw fluid into said second syringe ata rate related to the negative change in sensed pressure.
 11. Themedical injector of claim 1, further comprising a hand-operated movementcontrol comprising a lever movable between a home position and forwardend reverse positions; said control circuit responding to forwardmovement of said lever by moving said plunger drive ram into said secondsyringe to expel fluid from said second syringe at a rate related to theamount of forward movement of said lever from said home position, saidcontrol circuit responding to reverse movement of said lever by movingsaid plunger drive ram out of said second syringe to draw fluid intosaid second syringe at a rate related to the amount of reverse movementof said lever from said home position.